The present invention relates to a new configuration for the dimples on a golf ball surface which improve the flight characteristics of the ball.
According to the United States Golf Association (U.S.G.A.) rules, a golf ball may not have a weight in excess of 1.620 ounces or a diameter smaller than 1.680 inches. The initial velocity of balls conforming to U.S.G.A. regulations may not exceed 250 feet per second with a maximum tolerance of 2%. Initial velocity is measured on a standard machine kept by the U.S.G.A. A projection on a wheel rotating at a defined speed hits the test ball, and the length of time it takes the ball to traverse a set distance after impact is measured. U.S.G.A. regulations also require that a ball not travel a distance greater than 280 yards when hit by the U.S.G.A. outdoor driving machine under specified conditions. In addition to this specification, there is a tolerance of plus 4% and a 2% tolerance for test error.
These specifications limit how far a struck golf ball will travel in several ways. Increasing the weight of a golf ball tends to increase the distance it will travel and lower the trajectory. A ball having greater momentum is better able to overcome drag. Reducing the diameter of the ball also has the effect of increasing the distance it will travel when hit. This is believed to occur primarily because a smaller ball has a smaller projected area and, thus, a lower drag when traveling through the air. Increasing initial velocity increases the distance the ball will travel.
Drag on a golf ball is also reduced by forming a plurality of dimples, often circular, in the outer surface of the ball. The dimples serve to reduce the pressure differential between the front and rear of the ball as it travels through the air.
Numerous dimple configurations for use on golf balls are well-known in the patented prior art, including contoured dimples. For example, the Lu U.S. Pat. No. 5,503,398 discloses a golf ball having a plurality of dimples arranged on the spherical outer surface thereof, each of the dimples including a series of overlapping scales extending inwardly on an arcuate shaped sidewall surface of the dimple. The ball has improved directional control and increased lift and flight distance. The Oka U.S. Pat. No. 5,005,838 discloses a golf ball having a plurality of dimples in its outer surface. Each of the dimples includes a circular projection positioned in a bottom portion thereof. The projections are alleged to increase the coefficient of drag as the ball passes through the air, thereby decreasing the distance the ball will travel.
As opposed to the Oka golf ball, the present invention was developed in order to provide a golf ball with reduced drag so that the ball will travel a greater distance than conventional golf balls having circular dimples.
Accordingly, it is a primary object of the present invention to provide a golf ball having a spherical surface including a plurality of dimples arranged in the surface. The dimples are concavities in the ball surface at least some of which are modified so that part of the dimple surface is convex with respect to the dimple concave surface. Thus, these dimples have a raised contoured surface relative to the dimple bottom, with the contoured surface remaining below the surface of the ball.
According to another object of the invention, the contoured portion has a crescent configuration relative to the bottom surface. The contoured portion may comprise portions of different depths. The depth of a dimple at any point is the distance between the original undimpled ball surface and that point measured along a ball radius. In one embodiment the contoured portion includes a spaced pair of first portions having a first depth and a second portion arranged between the first portions and having a second depth different from the first depth. The contoured portion may also cover the entire bottom surface of the dimple.
According to a further embodiment, the contoured portion of at least one dimple is arranged adjacent to the contoured portion of an adjacent dimple.